The overall goal of this grant application is to determine the mitochondrial mechanism and relative neuroprotective potency of a panel of non-feminizing estrogen-like, estratrienes, using a structure-activity relationship (SAR) approach. These compounds are selected from novel compounds synthesized in our Drug Synthesis Core as well as more than 60 estratrienes discovered during the previous funding period to be potent neuroprotectants, but to lack interaction with either ERalpha or ERbeta. The estratrienes will include compounds more potent and compounds less potent than 17 beta-E2. This goal will be achieved by addressing 5 specific aims. Specific Aim will determine the SAR of neuroprotection and mitochondrial membrane potential (delta-psi) in two cell types in vitro. Specific Aim 2 will determine the SAR of neuroprotection and Ca 2+ increase in cytosol and mitochondria of two cell types in vitro. Specific Aim 3 will determine the SAR of neuroprotection and blockade of activation of cyclin dependent kinases in an in vivo model for cerebral ischemia-reperfusion. Specific Aim 4 will determine the SAR of neuroprotection and tau hyperphosphorylation in an in vivo model for cerebral ischemia-reperfusion. Transient middle cerebral artery (MCA) occlusion will be used to activate tau hyperphosphorylation and the potency of estratrienes in neuroprotection and blockade of tau hyperphosphorylation will be determined. Finally, Specific Aim 5 will determine the SAR of neuroprotection and tau hyperphosphorylation/ neurofibrillary tangle (NFTs) in an in vivo model using local cortical transduction of human mutated tau (p301L) and cerebral ischemia-reperfusion. Collectively, achieving these specific aims requires coordination with the Vector Core (Core B), the Neuroimaging Core (Core C), and the Drug Synthesis Core (Core D) and will substantially advance our understanding of the potential for clinical development of estratrienes for the prevention/treatment of Alzheimer's disease. The need for this research program is critical, given the recent WHI reports of prothrombic and carcinogenic toxicities of PremPro(R) in elderly women. There is a critical need for the discovery of potent, non-feminizing estrogens in the management of post-menopausal hormone-deprivation syndrome.